Injection molding is a manufacturing process for producing parts through injection of a material into a mold. Injection molding can be performed with many different materials such as metals, thermoplastic polymers, thermoset polymers, glasses, confections, and many other materials.
The most common material utilized for such processes are thermoplastic polymers and elastomers, usually employed to produce common plastic parts, tools, and toys. The process of injection molding of thermoplastic polymers includes melting a given material and forcing it into a mold cavity and allowing it to cool. Parts such as car fenders and bumpers are commonly a product of the injection molding process.
In-mold decoration (“IMD”) is a special type of injection molding that is used to apply a graphical or colorful aspect to the molded structure. Some applications also result in an abrasion-resistant, UV resistant, and/or chemical resistant coating. In such an embodiment, a carrier layer containing the resistant coating is laid inside an open mold, prior to injection. The mold is closed, the material is injected, and the graphics and abrasion coating is transferred from the carrier layer and bonded to the injected material, creating a single part with the specialized coating. Use of the IMD process in a graphical or color application operates through a similar process.
While a convenient way to create a useful molded structure, the graphical or colored layer is subject to an external environment. Through IMD, a graphical layer is adhered to a given part, but when subjected to a given environment for long periods, the graphical layer rapidly deteriorates. This can be seen on items having an applied graphical layer left outside in hot or extremely cold temperatures for long periods of time, such as car parts, or underwater pool components. These parts deteriorate rapidly because they lack sufficient protection from their environment. This is due at least in part to oxygen or other contaminates in proximity to the graphic that oxidize or otherwise degrade the graphical layer applied. Even with a protective coating applied to the outside of the part a colored or graphical coating adhered through IMD will tend to deteriorate, because the edges of the part, where the individual coatings meet are not completely sealed and allow intrusion of damaging substances. This is especially true in a harsh, chemically treated underwater environment such as a pool or spa or molded plastic parts on a car parked in the desert. This occurs because either the graphical layer is not protected at all, only receives limited protection from a third thin layer sprayed, printed or flood applied to the outside of the graphic that is not well sealed at the edges, or the protective layer itself deteriorates over time.
In light of the above, it would be advantageous to provide a two-layer IMD product that completely and hermetically encapsulates a graphical layer between the inner and outer layers, completely protecting it from the external environment. It would be further advantageous to provide a method of manufacture to produce a two-layer IMD product that can withstand harsh, chemically treated environments such as a pool or spa.